Should I get a cot bumper?

Get an unpadded moses basket and not one with a padded liner as they have the same concerns as cot bumpers. A thin Moses basket lining is recommended (fsid)to allow air to circulate. You could also look for the (harmful) chemical free "Oeko-Tex" standard fabric in the moses basket. Oeko-Tex is an international standard popular in Germany, Sweeden, China etc. and are very strict to ban all harmful chemicals in fabric.

I didn't use bumpers as I'd heard they are a suffocation risk, and older babies can use them to climb out.

However, when we moved dd1 from crib to cot at 6.5months old, she kept getting her arms and legs stuck between the bars in her sleep. I found air wrap. It's a breathable, stretchy mesh strip that attaches with Velcro.

Dd slept with her face pressed into it and had no trouble breathing. As it's stretchy, it flattens if a child tries to stand on it and climb.

No, I've heard they're dangerous. DD has always slept right up against the side of the cot i.e. with her head pressed hard against it, but she's never once cried our or seemed to hurt herself. So - anecdotally, I know - I can't see that they are necessary.